Protein

Proteins are present in the muscle, skin, hair and every other body part or tissue. Protein is required in the body for building and repairing tissue, for making enzymes that assist with many of the chemical reactions in the body, and for the production of haemoglobin which carries oxygen in the blood.

The ‘building blocks’ of protein are amino acids made from carbon, hydrogen, oxygen, nitrogen and occasionally sulphur. Each protein is composed of a chain of amino acids with a specific number and sequence of amino acids. There are twenty amino acids which are either called essential (as they cannot be made in the body and must be consumed from the diet), or non-essential (so they are synthesised in the body). The body does not store amino acids so a daily supply is required from diet.

Recommended daily intake (RDI) for protein (g/day)

Age (years)

19+yrs

Women

45

Men

55

The RDI for protein should equate to 11-15% of the total energy consumed in diet. In reality the average New Zealand adult is consuming between 15-16% of their total energy as protein.

One gram of protein provides 17 kJ or 4 calories of energy. The amount of protein required in the diet changes during a person's life due to the different periods of growth and repair that each person experiences.

Food sources of protein

When choosing foods that are good sources of protein it is important to consider not only the amount of protein the food provides but also the quality of the protein present.

There are two types of proteins – incomplete and complete. ‘Complete’ proteins contain all the amino acids required to build new protein. Animal foods are considered to be complete proteins and some examples of good protein sources are meat, seafood, chicken, eggs, milk and milk products. However, plant foods such as legumes, cereals and nuts are considered to contain ‘incomplete’ protein. This means that a wide variety of plant foods required to ensure that vegetarians receive all the amino acids required in the body for building protein.

When choosing foods as a protein source, we need to be aware of the other components present in the food. Often high-protein foods are also high-fat foods, especially meat sources of protein. Choosing foods from both plant and animal sources should give a high protein intake without dramatically increasing fat intake.

Eating advice

Protein in the diet is provided by a wide range of available foods, including lean meat, chicken and seafood, eggs and milk. Bread is also an important source.

If vegetarian, include protein from diverse plant sources, such as breads, cereals, legumes, and nuts. If lacto-ovo-vegetarian make sure eggs and milk products are included in the diet.

Bread & protein

Bread is an important source of protein in the New Zealand diet, providing 11% of the total protein in our diet. On average, protein present in bread ranges from about 8-15 g protein per 100 g bread dependent on the type of bread. Because bread is a cereal source of protein, it is important to combine bread with animal proteins, for example cheese or milk, to ensure that you are consuming a good source of complete protein and thus you are receiving all the amino acids required to build protein in the body.